In a wireless communication network, because wireless signal strength varies significantly depending on climate, location, distances between devices, obstacles therebetween, or the position of antennas. Thereby, when a signal arrives at the receiver, its signal strength cannot be predicted in advance. Hence, a wireless receiver needs an automatic gain controller (AGC) to make the signal received by the demodulator fall within an allowable range, and thus the receiver can operate normally.
There are two types of devices used for controlling gains: one is the variable gain amplifier (VGA), and the other is the programmable gain amplifier (PGA). According to device characteristics, the latter is easier to be implemented using a silicon tuner than the former is. However, the latter is less suitable for applications with continuous data transmission, such as a television system. Thereby, how to extend applications of a programmable gain amplifier has become a problem to be solved.